The larger in diameter the front tire is the better, to a point, for all the reasons mentioned above. Back in the early '80s, Honda used a 23" front tire on their XL500 and 250. I've never ridden one, so I don't know how well it worked, but they did go back to 21". With mountain bikes, 26" has been standard forever. But now many of the high dollar mountain bikes have gone to 29" wheels, and have used them for some time. I have never ridden a 29er, but most who have switched to them claim they are better. Anytime you have something turning, centrifugal force comes into play, and the more the weight, the higher the centrifugal force. This doesn't matter nearly as much on street bikes, but on dirt bikes, you want wheels that can stop and start turning with relative ease. Those big monster "adventure bikes" are meant mostly for road use, and occasional dirt road use. They are not trail bikes or MX bikes. I tend to think of them more like a pack mule, capable of carrying a lot of stuff over rough terrain at slow speeds, but no match for a race horse. You should choose your bike for the type of riding you intend to do. I have a cruiser for road riding, and an XT225 for off road riding.

Many cruisers also have a 21" front wheel, but it is only for looks. It actually hurts the handling, making the front end floppy. Mine has a 19" front wheel.